Founded in 1564 to highlight the statue of Neptune to which it owes its name, the square was the result of the expansion of the existing space between Palazzo d'Accursio and Palazzo del Podestà through the demolition of a block of buildings.

The statue of Neptune was built between 1563 and 1567 by the Flemish sculptor Jean de Boulogne, known as Giambologna, and by Tommaso Laureti, known as Il Siciliano.

On one side of the square is the Sala Borsa, since 2001 the Multimedia Civic Library, on the other, next to Palazzo del Podestà, stands Palazzo Re Enzo.